Induction heating



April 1962 N. v. ROSS ET AL 3,031,555

INDUCTION HEATING Filed July 15, 1959 INVENTORS. /V/CHOAAS V. FossM/ALTEE VANGfL OFF mental.

United States Patent O This invention relates to the continuous heatingof strip material such as relatively thin sheet metal by means ofinducing electrical current to flow therethrough. More 7 particularly,this invention relates to an inducting device comprising a continuousconductor element which is formed to provide a loop or opening throughwhich the strip material is continuously fed at a predetermined rate.Electrical current at a suitable frequency is provided to the conductorelement which induces current in the strip material causing the same tobe heated according to well known principles.

In inductors of this type, greater efiiciency can be obtained byoffsetting the upper and lower portions of the conductor relative to oneanother which results in a more effective flux threading area. However,prior devices of this type have the disadvantage that in the heating ofstrip the induced currents tend to crowd at the strip edges with theresult that said edges become overheated as compared with the center ofthe strip.

This adversely effects the strip by causing it to buckle or warp, and inextreme instances, overheating can cause the edges to melt. When theinductor is used for drying or bonding, the non-uniform heating isextremely detri- A primary object of this invention is to provide aninducting device which will result in more uniform heating across thestrip.

Another object of this invention is to provide a device of the abovetype capable of efiiciently heating very thin strip material at lowerfrequencies than heretofore thought possible.

A further object of this invention is to provide such a device which issimple in structure, is economical in production, and is highlyefiicient in use.

Other objects of the invention and the invention itself will beunderstood from the following description and the accompanying drawings,in which said drawings:

FIG. 1 is a top plan view of the inductor device of this inventionshowing strip material passing therethrough;

FIG. 2 is a section view taken along the line 2-2 of FIG. 1;

FIG. 3 is a section view taken along the FIG. 1;

FIG. 4 is a view similar to FIG. 1 showing a modified form of thepresent invention;

FIG. 5 is a section view taken along the line 55 of FIG. 4; and

FIG. 6 is a diagrammatic plan view of the inductor image showing thecurrent path, induced thereby.

Referring now to the figures of the drawings in all of which like partsare designated by like reference characters, and particularly to theembodiment of FIGS. 1-3, at 10 we show a single turn inductor adapted topass completely around a longitudinally moving strip 5. The inductor 10comprises a single, continuous conducting element which forms anuppermost conductor 11 spaced slightly above the strip and a lowermostconductor 12 spaced slightly below said strip. The ends of theconductors 11 and 12 are joined at one end thereof by means of adiagonal connector 13 which is spaced slightly laterally from the edgeof the strip and passes downwardly and rearwardly from the upper to thelower conductor. The opposite ends of the conductors 11 and 12 areprovided with short diagonal portions 15 and 16 which terminate in theplane of the strip in two laterally line 33 of "ice projecting, parallelterminals 17 and :18. Current for the inductor 10 is provided in anysuitable manner such as through a transformer 20 at the desiredfrequency which would be determined by the thickness of the strip 5.

By referring to FIG. 1, it will be noted that the uppermost conductor 11is positioned at right angles to or transversely of the edge of thestrip 5 at the medial portion 11c thereof and that it is provided at theends thereof with obliquely directed portions 11a and 11b which aredirected laterally and forwardly, the portion 11a connecting with theupper end of the diagonal connector 13 and the portion 11b connecting tothe short diagonal portion 15. The conductor 12, which is positionedbelow the strip 5, is similarly provided with a medial region 12c andwith laterally and rearwardly directed oblique portions 12a and 12bconnecting with the lowermost and rearwardly directed end of thediagonal connector 13 and with the short diagonal portion 16respectively. t will be further noted that the upper conductor 11including the medial region and the oblique portions 11a and 11b lie ina common plane spaced above the strip 5 and that the lowermost conductor12 including the medial region 12c, and the oblique portion 12a and 12blie in a common plane spaced slightly below the strip 5. The diagonalconnector 13 passes downwardly and rearwardly from the conductor 11 tothe conductor 12 at one end of the said conductors and the shortdiagonal portions 15 and 16 pass downwardly and upwardly respectivelyand are united with the terminals 17 and 18 at the other end of saidconductors.

By referring to FIG. 3, it will be seen that the conductors 11 and 12are offset relative to each other thereby obtaining a more effectiveflux threading area than would be otherwise obtained if said conductorswere vertically aligned. The oblique portions Ila-11b and -121) preventthe induced current in the strip from flowing outwardly and crowding theedges of the strip whereby said edges would become overheated. Thepresent construction concentrates more of the effective flux toward thecenter of the strip whereby said center is relatively slightly moreheated than the edges.

This is demonstrated in FIG. 6, which shows diagrammatically the currentpaths which are induced in the strip 5 by the inductor 1G. Said currentpaths are designated x, y, and z wherein y represents the central andlargest path bounded by the conductors 11 and 12. The paths x and z arerelatively much smaller than the path y and can be made small enoughthat the currents cancel out leaving only path y to do the heating. Inthe diagram as shown, the path y defines the area of greatest heatconcentration, and due to the oblique portions 11a-11b and 12a-12b andthe manner in which they cross, said path y is confined to the laterallycentral area of the strip 5 and away from the edges thereof. The inducedcurrents are thereby prevented from crowding at the edges of the strip.

The heating pattern which is effected by the above described device isillustrated in FIG. 1 by means of the heat patterns designated a, b, andc. It will be understood that the strip 5 is moving in the directionindicated by the arrow d. When any given transverse section of the strippasses immediately from under the inductor it the heat pattern will besubstantially as illustrated at a wherein the forwardly curved portionof the pattern indicates that more heat is present in the centralportion of the strip than is to be found at the edges thereof. As thesame section proceeds to the area indicated by the heat pattern b, itwill be noted that said pattern begins to flatten out transversely ofthe strip whereby the edges and the center of said strip attain moreuniform temperatures. As said section moves on to the area of the heatpattern indicated at c, the temperature will have 3,0 3 become"equalized whereby it is uniform across the entirewidth of the strip.

It will be readily seen that with the device of the present invention,overheating of the edges is eiiectively pre- "vented and uniformtemperature across the width of the strip is attained shortly after thestrip passes the inductor 10. The result is an over-all greaterefiiciency in heating and makes .possible the efiicient heating ofthinner strip at a .lower relative frequency than has been heretoforethought possible.

FIGS. 4 and 5 illustrate amodification of the invention of FIGS. 1-3wherein a multiple turn inductor 39 is utilized and is formed by asingle conducting element which passes around the strip 25 more thanonce. Each turn of the conductor element around the strip 25 comprises apattern or form similar to that of FIG. 1, each subsequent turn beingspaced slightly from the previous turn and being co-planar therewith.The first turn of the :inductor comprises an upper conductor 31 havingobliquely directed portions 31a and 31b and a lowermost conductor 32having oppositely directed oblique portions 32a and 32b. The conductors31 and 32 are connected across the plane of the strip and beyond theedge thereof by means of a diagonal connector 33 at one end. Theopposite end of the conductor 32 is connected through a diagonalconnector 34 to a second, uppermost conductor 35 having obliquelydirected portions 35a. and 351; which are parallel with but spaced fromthe obliquely directed portions 31a and 31b respectively. The upperconductor '35 is connected to a lower conductor 36 having obliquelydirected portions 36a and 36b. This latter connection is made by meansof a diagonal connector 37 which is positioned parallel with and spacedfrom the diagonal connector 33. The upper conductor 31 and the lowerconductor '36 are provided with laterally directed, straight terminalportions 39 and 40 connected to a suitable source of current such as atransformer 41 as provided in'the first embodiment of our invention.

invention may be made, such as changes in size and dimension, without,however, departing from the spirit thereof or the scope of the appendedclaims.

What we claim is:

1. An inductor device for heating strip material comprising a singleconducting element passing around said strip and spaced therefrom, saidconducting element comprising upper and lower transverse conductorspositioned respectively above and below said strip, and extending beyondthe edges thereof, said conductors being parallel with said strip andhorizontally offset along the longitudinal dimension of said strip,portions adjacent the ends of each conductor being obliquely directed ina horizontal plane in the direction of the other conductor and passingacross the edges of said strip, a diagonal connector portion connectingsaid conductors adjacent one edge of said strip, said conductorsconnected to a source of electrical current adjacent the opposite edgeof said strip.

2. An inductor device for heating strip material cornprising acontinuous conducting element formed to provide at least one turn aroundsaid strip, said conducting element comprising upper and lowerconductors spaced respectively above and below said strip in planesparallel to said strip, said conductors having transversely disposedmedial portions and obliquely angled end portions lying in a commonplane, said end portions of each said conductor being angled in a commonlongitudinal direction relative to said strip and the end portions ofsaid upper conductor being oppositely directed from that of said lowerconductor, said upper and lower conductors so disposed that verticalplanes defined by the end portions of said upper conductor intersectvertical planes defined by the end portions of said lower conductor.

3. An inductor device for heating strip material comprising a continuousconducting element having a plurality of turns passing around saidstrip, said conducting element comprising upper and lower conductorsspaced respectively above and below said strip in planes parallel tosaid strip, said conductors having transversely disposed medial portionsandobliquely angled end portions disposed in a common plane, saidobliquely angled end portions of each said conductor being angled in acommon longitudinal direction relative tosaid strip and the end portionsof said upperconductors being oppositely directed from those of saidlower conductor, :the upper and lower conductors of each said turn beingso disposed that vertical planes defined by the end portions of theupper conductor of said turn intersectivertical planes defined by theend portion of the lower conductor otthe same said turn.

4. An inductor device for heating'strip material comprising aconductor'spaced vertically from said strip and extending outwardlybeyond the edges of said strip, the portions of said conductor whichpass over the edges'of said strip beingpositioned obliquely relative tosaid edges disposed in a common plane to amedial portion thereof, andthe medial portion of saidconductor being positioned transversely and atrightangles to the edges of said strip.

5. An inductor device for heating strip material comprising a conductorspaced vertically from said strip'and extending outwardly beyond theedges of said strip, the portions of said conductor which pass over theedges of said strip being in a plane parallel to the plane of the stripand directed obliquely relative to said edges, the medial portions ofsaid conductor beingpositioned in the same plane as said obliquelydirected portions.

'6. An inductor device for heating stripmaterial comelement comprisingportions which extend outwardly beyond the edges of said strip, saidoutwardly extending References Cited in the fileofthis patent UNITEDSTATES PATENTS 2,897,328 Alf et a1 July 28, 1959

